Spot welding cap changer

ABSTRACT

The invention relates to a spot welding cap changer (1) with a cap puller (2) and two cap magazines (3, 3A), the cap puller (2) having a gripper (20) with spring-loaded, pivotable jaws (21, 22), which in response to a turning and axial pulling-off movement detaches a spot welding cap (K) of a pincer spot welding head introduced into it from a shaft of the pincer welding head in such a way that it is clamped to prevent it twisting, and the cap magazines (3, 3A) holding spot welding caps respectively in a round cap carrier (31) such that they are circularly arranged in a directed and oriented manner and are respectively transported individually one after the other into an access position against a stop (32) by an advancing force (P).

The invention relates to a spot welding cap changer with a cap extractor and two cap magazines, the cap extractor having a gripper with spring-loaded, pivoting jaws, which in response to a turning and axial extraction movement detaches a spot welding cap of a pincer spot welding head inserted into it from a shaft of the pincer welding head in such a way that it is clamped to prevent twisting,

-   -   and the cap magazines holding spot-welding caps in a cap carrier         in such a way that they are circularly arranged in a directed         and oriented manner and are one by one transported by an         advancing force against a stop, into an access position allowing         to attach them axially to the free shaft of the pincer and to         extract them with it.

Such a mechanical electrode cap changer is known from the DE 102 22 248 A1. It has a two-part cap extractor, accessible from both sides, in a body separate from the magazine.

Since gravity causes the caps to slide against a cap stop, the device can only be operated stationary in the vicinity of a mobile welding robot. Changing caps at a stationary pincer spot welding head, to which each component is fed by a robot for welding, is therefore not possible. The pincer spot welding heads/welding installations often have short shafts, which are for instance curved, so that the cap extractor, equipped with three large jaws and accordingly big, cannot be positioned for extraction.

It is the object of the invention to provide for an automatic faster and safer exchange of the spot welding caps both at mobile and stationary spot welding installations with a short access distance.

The solution resides in that

-   -   the cap extractor has two opposed grippers, each with jaws that         are open at their ends and can be rotated towards each other         with approximately parallel toothed grip surfaces whose distance         is slightly smaller than a diameter of a spot welding cap,     -   and each cap magazine contains a cap carrier, which, driven by a         spring box, presses by way of its advancing force one of the         caps respectively against the stop, and in the access position a         rim overlap overlaps the cap on one side.

Advantageous forms of the invention are indicated in the subclaims.

In the new embodiment the cap extractor and the magazine are mounted on a support which preferably is spring-mounted. In contrast to the known system, the new construction design gives the possibility not only to be used at welding robots, but also at stationary pincer welding heads or welding installations.

Compared with the known clamping system with three jaws, the new cap-extraction installation provides for shorter clamp and spin travels, therefore much shorter intervals for detaching the caps. Moreover, from the smaller design results a wider array of application, for instance at non-standard pincers or very short, curved shafts.

The two cap extractors are each open at the ends of the jaws and thus accessible to a cap. The jaws grip it directly by way of the undersize of their distance and detach the cap, whereby a rotation around an angle of about 30-60° suffices. This way a cap change is possible even in extremely narrow confines. Since the two grippers are oriented in opposite directions, respectively one of them is accessible from the various sides in a clockwise rotation, so that no turning of the pincer is necessary, even if the pincer shafts are screwed on.

Furthermore, the round magazine is much more compact than the straight magazine functioning by gravity of the known installation. It can be held and operated in any position because of the spring drive.

Furthermore, the two round magazines arranged on parallel axes provide in each case for an access with short radial travel to the access positions in the access openings. In an embodiment with a magazine cover, this cover is directly shifted during access, far enough to let the rim overlap uncover the cap frame, so that the detaching is possible. The example shows a radial infeed and an axial access of the shafts into the magazine.

Both partial devices, the cap changer, and the cap magazine, are mounted on a support close to one another, and thus can be set up stationary, or mounted to a robot arm in a fixed or detachable manner. In the first case the welding robot changes the caps of its own pincer, and in the second case the robot changes the caps at the stationary pincers or installations respectively by means of the device. The changing device at the robot arm is movably mounted, constantly ready for operation in a free space next to the gripper of the robot or on a guide rail, or it is located in a parking position, where it can be picked up and brought to operation by the gripper; this is called alternating pincer principle.

Advantageously, cap sensors are arranged on the device, which indicate whether a cap is in place or not. Moreover, the charging level of the magazines is monitored. This way it is ensured that after a cap change a cap is in place at the shaft of the pincer welding head before the cooling water is switched on. Furthermore it can be verified, whether the old cap was removed, when it is reported that there is no cap in place while the shaft is approaching.

The embodiment of the cap magazine without a cover holds the welding caps in an elastic cap carrier in a close fit, axially movable by propulsive or tractive force.

Advantageous embodiments are represented in the FIGS. 1 to 6.

FIG. 1 shows the entire device schematically and in perspective;

FIG. 2 shows a transparent top view of the cap extractor;

FIG. 2A, 2B show detailed enlargements of the grip surfaces;

FIG. 3 shows a perspective of the cap extractor;

FIG. 4 shows a cap magazine in perspective, closed, enlarged

FIG. 5 shows a cap magazine in perspective, open, enlarged

FIG. 6 shows a top view of the magazine cover.

FIG. 1 shows a complete spot welding cap changer 1, which is movably held on a support rail 5 at a robot arm. Alternatively, it is firmly mounted with the mounting plate 50. The bilaterally equipped cap extractor 2 is bolted at the free end of the mounting plate 50, with the two grippers 20 respectively on the sides, their direction opposite to one another. Pulled off caps K are depicted between the jaws 21, 22, after being detached at the rim of a storage container they drop into it.

Offset to the rear from the cap extractor 2 respectively one cap magazine 3, 3A laterally offset to the other is mounted on the mounting plate 50, with the magazine cover 4 respectively directed laterally and the access openings 40 oriented axially parallel to the extracted welding caps K that are still held by the gripper, so that the shafts of the pincer spot welding head have to travel only short distances while changing the caps.

FIG. 2 shows a top view on the cap extractor 2, which consists of very few parts. The grippers 20 are composed of one fixed, toothed jaw 21 respectively, and one jaw 22 which is mounted in such a way that it can be pivoted towards said jaw 21. The pivot joint 24 is located behind the fixed jaw 21 by way of a U-shaped structure of the movable jaw arm 25, so that a cap K positioned in the gripper 20 will be clamped at a twist depending on the direction of rotation.

The initial pressing force of the jaws 21, 22 is caused by a bracing spring 26, which for example, is formed as a spiral or bracing spring with spread ends, each pressing against a jaw arm 25.

On the infeed side the grippers 20 are provided with infeed skews 27, 28. From these extend the roughly parallel grip surfaces 23, each with a toothing in opposite direction 29A, 29B, as FIGS. 2A and 2B show in partial view and in detail. If there is no cap K inserted in the grippers 20, then the distance A of the grip surfaces 23 has a minor undersize compared to the cap outside diameter D.

FIG. 3 shows that the spring 26 and the movable jaws 21, 22 as well as a jaw plate 62, on which the fixed jaws 21 are formed, are held between two cover plates 60, 61. The jaw plate 62 has a corresponding cavity, in which the U-shaped jaw arms 22 have free space to move.

FIG. 4 shows a round cap magazine 3, which consists of a barrel shaped cap carrier 31, closed with a magazine cover 4, whereas a radial section remains free up to the rounded access opening 40, in which a welding cap K in the withdrawal position is pressed to the edge of a stop 32 at the cover.

The cover 4 has a small rim overlap 41 of the cap frame in the curve of the access opening 40, an induct skew 42 connecting to said rim overlap which is cascaded to the top side of the cover. At an embodiment with a hinged cover 4, a slot 43 is formed, through which reaches a bracket 34, bevelled on the outside, which keeps the cover shut.

On the other side of the access opening 40 a hinge 44 with a slotted hole 45 is formed in the extension level of the cover, the cones 46 of said hinge being held in a hinge support 47.

FIG. 5 shows the open round magazine 3 with a hinge and equipped with a welding cap K in the drill holes 30 of the cap carrier 31, the cap K protruding by a few millimeters. A firmly mounted spring box 33, schematically depicted, is in the centre of the cap carrier 31, said spring box carrying the bracket 34 so that it can be radially moved. A preloaded spindle or spiral spring is arranged centrally in the spring box 33, one end of the spring being fixed to the spring box 33, the other to the cap carrier 31, so that the latter is pressed with a torsion force P in the direction of the stop 32, which extends radially on the magazine cover.

The plate-shape bracket 34 extends in a diagonal guiding slot on the cover of the spring box 33. In the closed state, as shown here, a compression spring arrangement 35, held in the cover, extends from the bracket 34 and is supported by means of a support pin 36 on the rounded hinge support 47, and presses the bracket 34 in the closed position, in which it overlaps the cover 4 in the closed state and holds the rim overlap 41 in the overlap position, the cone 46 being in the rear stop position in the slotted hole 45, as FIG. 1 shows. To open the cover 4, the bracket 34 is pushed back manually. Alternatively, the round magazine can be implemented without a hinge for the opening of the cover. In this case the cover is only held in a movable manner, so that the shaft of the pincer, when inserted, slides the cover by the skew 42 to release the rim overlap.

FIG. 6 shows a top view on the magazine cover 4, whose main outline consists of two semi-circles with shifted centres M1, M2, whereby on one side the access opening 40 extends in the direction of the centre, and on the opposite side the hinge 44 extends on the outside. The slot in the cover 43 extends 4 in the central area in the direction between the access opening 40 and the hinge 44. The bracket 34 in the cover and in the fixed spring box 33 is guided in this direction. The cover 4 is about 15 mm high and largely hollow shaped and has a stiffening cover rim 48, which passes into the stop 32 and on the other side into the hinge 44. The cover 4 is lowered at the induct skew 42 by about 5 mm to the infeed area. Internally, the cover surface drives the caps to the withdrawal level when turned in the stop position. A chamber 49, which contains the compression spring arrangement 35, is represented with a dashed outline.

The compact construction of the cap extractor with the magazines allows for a significant reduction of the changing times, for example, from 22 to 17 sec, which corresponds to about 23%.

LIST OF REFERENCE SIGNS

1 spot welding cap changer

2 cap extractor

20 gripper

21, 22 jaws

23 grip surfaces

24 pivot joint

25 jaw arm

26 bracing spring

27, 28 infeed skews

29A, 29B toothing

3, 3A cap magazine

30 drill holes

31 cap carriers

32 stop

33 spring box

34 bracket

35 compression spring

36 support pin

4 magazine cover

40 access opening

41 rim overlap

42 induct skew on the cover

43 slot in the cover

44 hinge

45 slotted hole in the hinge

46 cones

47 hinge support

48 cover rim

49 compression spring chamber

5 support rail

50 mounting plates

60, 61 cover plates

62 jaw plate

A gripping jaw distance

D outside diameter of the caps

K cap

P advancing force

M1, M2 semicircle centres 

The invention claimed is:
 1. A cap magazine for spot welding, the cap magazine comprising: a cap carrier having a plurality of holes; a plurality of spot welding caps received in the plurality of holes; wherein each of the plurality of holes has a bottom wall that inhibits the spot welding caps from passing therethrough, and each spot welding cap has a portion that protrudes outwardly beyond an upper surface of the cap carrier; a spring for driving the cap carrier without directly contacting the caps, the spring advancing the caps one by one so that the portion of one of the caps that protrudes beyond the upper surface of the cap carrier bears against a stop at an access position at which one of the spot welding caps can be attached axially to a shaft of a pincer spot welding head and pulled from the cap carrier, and when the cap in the access position is extracted from the cap carrier, the spring advances another one of the caps into the access position.
 2. The cap magazine of claim 1, wherein the cap changer is movably held at a robot arm.
 3. The cap magazine of claim 1, wherein after being detached, the spot welding caps are dropped into a storage container.
 4. The cap magazine of claim 1, wherein the cap extractor is offset from the cap magazine.
 5. The cap magazine of claim 1 further comprising a cover that covers all but the cap in the access position, wherein the cover is directed laterally and the access opening is oriented axially parallel to the extracted welding caps.
 6. The cap magazine of claim 1, wherein the spot welding cap in the access position is pressed to the edge of the stop.
 7. The cap magazine of claim 1, wherein a height of the stop is less than a height of the spot welding cap.
 8. The cap magazine of claim 1, wherein the cap magazine is held and operated in any position because of the spring drive.
 9. The cap magazine of claim 1, further comprising cap sensors for indicating whether a cap is in place or not.
 10. The cap magazine of claim 1, further comprising cap sensors for monitoring the charging level of the magazine.
 11. The cap magazine of claim 10, wherein the sensors ensure that after a cap change, a cap is in place at the shaft of the pincer welding head before cooling water is switched on.
 12. The cap magazine of claim 1, further comprising sensors arranged at the cap magazine, which send a signal to a control device when a predetermined remaining quantity of spot welding caps is in stock in the cap magazine.
 13. A spot welding cap changer comprising: a gripper for removing a spot welding cap from a pincer spot welding head; and a cap magazine for spot welding, the cap magazine comprising: a cap carrier having a plurality of holes; a plurality of spot welding caps received in the plurality of holes; wherein each of the plurality of holes has a bottom wall that inhibits the spot welding caps from passing therethrough, and each spot welding cap has a portion that protrudes outwardly beyond an upper surface of the cap carrier; a spring for driving the cap carrier without directly contacting the caps, the spring advancing the caps one by one so that the portion of one of the caps that protrudes beyond the upper surface of the cap carrier bears against a stop at an access position at which one of the spot welding caps can be attached axially to a shaft of a pincer spot welding head and pulled from the cap carrier, and when the cap in the access position is extracted from the cap carrier, the spring advances another one of the caps into the access position.
 14. The spot welding cap changer of claim 13, wherein the cap exchanger includes two magazines arranged on parallel axes.
 15. The spot welding cap changer of claim 13, wherein the two magazines are positioned to face opposite each other.
 16. The spot welding cap changer of claim 13, wherein the cap changer is in a fixed or detachable manner.
 17. The spot welding cap changer of claim 13, wherein a welding robot changes the caps of its own pincer.
 18. The spot welding cap changer of claim 17, wherein the cap changer is moveably mounted in a free space next to the gripper of the robot.
 19. The spot welding cap changer of claim 13, wherein the cap changer is located in a parking position, where the cap changer is picked up and brought to operation by the gripper. 